[minor] avoid function call to get globalzk (apache#6667)

Co-authored-by: Sijie Guo <[email protected]>

pulsar-broker/src/main/java/org/apache/pulsar/broker/PulsarService.java

@@ -637,7 +637,7 @@ protected void startZkCacheService() throws PulsarServerException {
             throw new PulsarServerException(e);
         }
 
-        this.configurationCacheService = new ConfigurationCacheService(getGlobalZkCache(), this.config.getClusterName());
+        this.configurationCacheService = new ConfigurationCacheService(globalZkCache, this.config.getClusterName());
         this.localZkCacheService = new LocalZooKeeperCacheService(getLocalZkCache(), this.configurationCacheService);
     }